1. Field of the Invention
The present invention relates to an output shaft assembly, which has a clutch arrangement, and also relates to a motor apparatus and a wiper motor apparatus, which have such an output shaft assembly.
2. Description of Related Art
For example, in a vehicle power window system for driving a window glass of a vehicle door or in a vehicle sunroof system for driving a sunroof lid, a motor apparatus is used as a drive source.
Japanese Unexamined Utility Model Publication No. H05-3654 discloses a motor apparatus, which has a speed reducing mechanism that decelerates rotation of a motor main body. The speed reducing mechanism includes a worm gear and a worm wheel. The worm gear is provided to an end of a rotatable shaft of the motor main body to rotate integrally with the rotatable shaft. The motor apparatus is used to drive the sunroof lid of the sunroof system. A friction clutch device (a friction clutch arrangement) is provided to an output shaft of the motor apparatus. The friction clutch device includes a friction member and a disk plate. The friction member is integrally formed in the worm wheel, and the disk plate is connected to the output shaft to rotate integrally with the output shaft. Furthermore, the disk plate is urged against the friction member by a spring to form frictional engagement between the disk plate and the friction member. In a normal operation, rotation of the motor main body is supplied to the friction clutch through the engagement between the worm gear and the worm wheel. Then, this drive force is transmitted through the frictional engagement between the friction member of the worm wheel and the disk plate, so that the output shaft connected to the disk plate is rotated integrally with the worm wheel to drive a sunroof lid. When an object is placed in a moving path of the sunroof lid, movement of the sunroof lid is stopped by the object to lock the output shaft. At this time, the friction member is slid relative to the disk plate, so that the worm wheel is rotated relative to the output shaft.
In this way, it is possible to limit damage to each component, such as the worm wheel, and also possible to limit burnout of the motor main body.
This kind of clutch device is also preferred in the vehicle wiper system. For example, in the wiper system, at the time of wiping a window glass by a wiper blade of a wiper, when heavy snow, which has been accumulated on a roof of the vehicle, falls onto the wiper blade and a wiper arm connected to the wiper blade, the wiper blade and the wiper arm are arrested by the fallen heavy snow or receive an excessively large external force from the fallen snow. Therefore, the excessively large external force is applied to corresponding components of the wiper system. When the above clutch device is provided in the wiper system, it is possible to limit damage to the corresponding components of the wiper system or to limit burnout of the motor main body. Furthermore, a strength of each corresponding component does not need to be set upon consideration of the excessively large external force.
However, in the previously proposed clutch device recited in Japanese Unexamined Utility Model Publication No. H05-3654, the spring is used to urge the disk plate against the friction member to generate the frictional resistive force. The spring is rotated together with the disk plate or is slid relative to the disk plate. In the former case, the spring rotates together with the disk plate, and the spring is slid relative to a support structure. In the latter case, the spring does not slid relative to the support structure but is slid relative to the disk plate. In each of these cases, at the time of driving the motor main body, when rotation of the motor main body is transmitted to the output shaft through the clutch device, a sliding loss of the spring occurs to reduce a transmission efficiency of the rotational force. Furthermore, a substantial noise could be generated due to the sliding movement.
In the above clutch device, at the time of locking the output shaft, the worm wheel (the driving side) is rotated relative to the output shaft (the driven side) to limit damage to the corresponding components. However, the performance is sacrificed to cause a reduction in the transmission efficiency of the rotational force and/or generation of the noise.
Furthermore, in the case of Japanese Unexamined Utility Model Publication No. H05-3654, when the components of the clutch device are installed to a housing of the motor apparatus one after another, an entire assembly operation of the motor apparatus is lengthened. Thus, it is desirable to provide the clutch device in a form of a sub-assembly of the motor apparatus, such as an output shaft assembly, in which the clutch device (or the clutch arrangement) is integrated with the output shaft of the motor apparatus. When the clutch device is preassembled as the output shaft assembly, the clutch arrangement can be simultaneously installed to the motor apparatus at the time of installing the output shaft. Thus, an entire assembly time of the motor apparatus can be shortened. Furthermore, when the clutch device is preassembled as the output shaft assembly, handling of the clutch device can be eased during, for example, transporting of the output shaft assembly from one assembling stage to another assembling stage of the motor apparatus since it is formed as a single component or a single assembly.
Apart from the above case, Japanese Unexamined Patent Publication No. H09-118202 discloses another wiper motor apparatus, which includes a worm wheel, a swing arm and a joint member. The worm wheel is meshed with a rotatable shaft of an armature, which is rotatably supported by a case. The swing arm is connected to a wiper shaft. One end of the joint member is connected to a predetermined point of the worm wheel, and the other end of the joint member is connected to the swing arm. Upon energization of the wiper motor apparatus, the armature is rotated to rotate the worm wheel. Then, the rotation of the worm wheel is converted to a swing motion of the swing arm through the joint member to reciprocally rotate the wiper shaft. Therefore, a wiper arm, which is directly installed to the wiper shaft, is swung to wipe a window glass of the vehicle.
Similar to the above case, in the non-operating state of the wiper where a wiper blade connected to the wiper arm is stopped and is thus held substantially parallel to a lower edge of the glass surface, when an external force, which is exerted by, for example, heavy snow, is applied to the wiper blade and the wiper arm, the wiper blade and the wiper arm are pressed downward beyond a lower turning point. At this time, the wiper shaft and the swing arm of the wiper motor apparatus are rotated further beyond a normal reciprocal rotational angular range. Therefore, the joint member, which is connected to the swing arm, or the worm wheel, which is connected to the joint member, could be damaged by the external force.
Thus, to limit the damage of the above components and to limit rotation of the wiper arm into a vehicle body region beyond the window glass area of the vehicle, in the wiper motor apparatus disclosed in Japanese Unexamined Patent Publication No. H09-118202, a rotational range limiting portion is provided at a location, which is outside of the normal reciprocal rotational angular range of the swing arm to limit the rotation of the swing arm beyond the predetermined reciprocal rotational angular range of the swing arm.
However, an excessively large external force could be applied to, for example, the wiper blade and the wiper arm even in a case where the wiper blade and the wiper arm are not placed outside of the predetermined reciprocal rotational angular range. In other words, the excessively large external force could be applied to, for example, the wiper blade and the wiper arm even in the case where the wiper blade and the wiper arm are operated within the predetermined reciprocal rotational angular range (a normal wiping range). This could be a case where heavy snow, which has been accumulated on a roof of the vehicle, falls onto the wiper blade and the wiper arm, which is operated and is located in the normal wiping range other than the lower turning point. In such a case, the wiper blade and the wiper arm are arrested by the fallen heavy snow or receive an excessively large external force from the fallen snow. Therefore, the excessively large external force is applied to the swing arm, the joint member, the worm wheel and/or the worm gear through the wiper shaft, so that these components could be damaged by the excessively large external force. Thus, the above-described disadvantage still exists.
Therefore, in the case of the wiper motor apparatus described in Japanese Unexamined Patent Publication No. H09-118202, each corresponding component of the wiper motor apparatus needs to be designed to withstand the above described excessively large external force.